1. Technical Field of the Invention
The present invention is directed to a deinking agent for use in reclaiming wastepapers such as newspapers, magazines, leaflets and office automation wastepapers. More particularly, the present invention is directed to a deinking agent where deinked pulp having a low Eric number (residual ink fines) can be obtained at a high removal rate of residual ink fines during the flotation step.
2. Background of the Invention
Although newspapers, magazines, office automation wastepapers, etc. have been recycled, effective utilization of wastepapers has recently become increasingly important in connection with global environmental problems such as protection of forest resources and refuse disposal. Utilization of wastepapers has also increasingly been made for deinked pulp, including use of pulp where a medium-duty paper is made from newspapers. Recently, from the standpoint of deinking in keeping with changes in printing techniques, printing methods, printing ink components, etc., wastepapers have been getting into more and more severe circumstances. In view of this, improvements in equipment have been made for the purpose of promoting deinking. Conventional chemicals which have been used in order to separate and remove ink and other impurities from wastepapers include, alkali agents such as sodium hydroxide, sodium silicate, sodium carbonate, and sodium phosphate; bleaching agents such as hydrogen peroxide, hyposulfites, and hypochlorites; sequestering agents such as EDTA and DTPA; and deinking agents, examples of which include anionic surfactants such as salts of alkylbenzenesulfonic acids, salts of higher alcohol sulfates, salts of .alpha.-olefinsulfonic acids and dialkylsulfosuccinate and nonionic surfactants such as higher alcohols, ethylene oxide adducts of alkylphenols and fatty acids, and alkanolamides, which may be used either alone or in the form of a blend of two or more thereof.
Among conventional deinking agents, however, those capable of providing overall performances for all deinked pulp have not been found out yet. For example, although higher fatty acids have been known as deinking agents having high ink-collecting performance, use of any higher fatty acid alone lets a large amount of unstripped ink and sticky matter remain in deinked pulp. Further, most of higher fatty acids become so solid at ordinary temperature that any solidified fatty acid and its salt such as its Ca salt, in particular, if left in a large amount in deinked pulp, become nuclei in the course of papermaking to give rise to scale contamination on a paper machine. The resulting paper is so slippery it causes problems in windup after treatment with a dryer, and the like. On the other hand, alkylene oxide adducts such as ethylene oxide or propylene oxide adducts have been found out to be so effective in improving the whiteness of deinked pulp that they are widely used as deinking agents even today. Since a difficulty in stripping ink has recently been increased in keeping with improvements in printing techniques, however, further improvements with respect to whiteness and removal of gray areas are desired.
In the foregoing background, various investigations have been made with the aim of obtaining deinked pulp having a higher whiteness and containing little residual ink. For example, JP-A 3-24126 discloses that deinked pulp having high whiteness can be obtained using an alkylene oxide adduct of a dimer acid or trimer acid having 20 to 36 carbon atoms. On the other hand, JP-A 3-152284 discloses that deinked pulp having high whiteness and containing little residual ink can be obtained using an alkylene oxide adduct of a specific dicarboxylic acid having a cyclic structure or a monoester of such a dicarboxylic acid. Further, JP-A 3-193986 discloses that deinked pulp having high whiteness and containing little residual ink can be obtained using an adduct of a partial ester prepared from a dimer acid and/or polymer acid of a higher unsaturated fatty acid having 16 to 20 carbon atoms and an alcohol having 1 to 18 carbon atoms with at most 300 mol of an alkylene oxide.
However, deinked pulp having a sufficiently low Eric number (residual ink fines) cannot easily be obtained even using any one of the deinking agents as disclosed in the above-mentioned publications. Thus, a further improvement in this respect is desired. The Eric number, which indicates the amount of ink fines remaining in deinked pulp, is an index for evaluation of removal of gray areas of deinked pulp. With the same whiteness, deinked pulp having a lower Eric number can be said to be deinked pulp of better quality with less color. Use of any one of deinking agents as disclosed in the above-mentioned publications, though able to improve the whiteness of deinked pulp, cannot lower the Eric number of deinked pulp, whereby the quality of the resulting deinked pulp is not satisfactory.